A known ball screw that can be used as a part of a linear drive mechanism comprises a screw shaft having an outer circumferential surface formed with a shaft thread, a nut main body having an inner circumferential surface formed with a nut thread opposite to the shaft thread to define a rolling passage in cooperation with the shaft thread, a ball return passage extending in an axial direction, and a deflector receiving recess formed on at least one end surface of the nut main body in continuation with the nut thread and defining an open end of the ball return passage, a plurality of balls received in the rolling passage and the ball return passage, and an end deflector received in the deflector receiving recess, the end deflector being provided with a ball passing passage for passing the balls between the rolling passage and the ball return passage, and a tongue guiding the balls from the rolling passage to the ball passing passage. The end deflector is fixedly secured to the nut main body by means of screws passed axially through the end deflector and threaded into the nut main body. See JP2007-24305A and JP2013-174316A, for instance.
In such a conventional ball screw, since the axial force caused by the fastening of the screws acts on the axial front end surface of the end deflector and the bottom surface of the deflector receiving recess upon which the front end surface of the end deflector abuts, and the fastening force of the screws is applied to the entire axial length of the end deflector as a compressive force, the end deflector is caused to deform over an wide region thereof, and this in turn may impair the positional precision of the ball passing passage and the tongue relative to the nut main body. Such an impairment of the positional precision may adversely affect the smooth operation of the ball screw.
This problem is particularly acute when the end deflector is made of plastic material, and is more prone to deformation than a deflector made of metallic material.